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# Mefenamic Acid
## Overview
Mefenamic acid is a fenamate-class nonsteroidal anti-inflammatory drug (NSAID). It exhibits analgesic, anti-inflammatory, and antipyretic properties via non-selective inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis.
## Primary Indications
* Primary dysmenorrhea.
* Mild to moderate acute pain (typically short-term usage, ≤7 days).
## Adult Dosing
* **Dysmenorrhea/Acute Pain:** 500 mg initially, followed by 250 mg every 6 hours as needed.
* **Maximum Dose:** Do not exceed 1,500 mg per day or use for longer than 7 consecutive days.
## Pediatric Dosing
* **Children ≥14 years:** Follow adult dosing guidelines (500 mg loading, then 250 mg every 6 hours).
* **Children <14 years:** Safety and efficacy have not been established. Use is generally not recommended in this population.
## Dose Adjustments
* **Renal Impairment:** Not recommended for use in patients with severe renal impairment. In mild to moderate impairment, use with extreme caution; monitor renal function closely.
* **Hepatic Impairment:** Use with caution; dose reduction may be required. Avoid in severe hepatic impairment.
* **Geriatric:** Increased risk of gastrointestinal (GI) toxicity and renal complications. Use the lowest effective dose for the shortest duration.
## Contraindications
* Known hypersensitivity (including aspirin or other NSAIDs).
* History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs.
* Active peptic ulceration or inflammatory bowel disease.
* Perioperative pain in the setting of coronary artery bypass graft (CABG) surgery.
* Severe renal or hepatic failure.
* Third trimester of pregnancy (risk of premature closure of the ductus arteriosus).
## Adverse Effects
* **GI:** Diarrhea (common and sometimes dose-limiting), nausea, dyspepsia, abdominal pain, GI ulceration/bleeding.
* **Renal:** Fluid retention, edema, acute kidney injury.
* **Cardiovascular:** Hypertension, increased risk of serious thrombotic events (myocardial infarction, stroke).
* **Hematologic:** Anemia, rare cases of hemolytic anemia with long-term use.
* **Dermatologic:** Rash, photosensitivity.
## Key Drug Interactions
* **Anticoagulants (e.g., Warfarin):** Increased risk of bleeding.
* **Antiplatelet Agents/SSRIs:** Increased risk of GI bleeding.
* **Antihypertensives (ACE inhibitors, ARBs, Diuretics):** Reduced antihypertensive effect; increased risk of nephrotoxicity.
* **Lithium/Methotrexate:** NSAIDs may decrease clearance, increasing serum concentrations and toxicity.
## Monitoring
* **Renal:** Monitor serum creatinine and BUN in high-risk patients.
* **GI:** Observe for signs of GI bleeding or ulceration (occult blood, abdominal pain).
* **Blood Pressure:** Regular monitoring, especially in patients with hypertension.
* **CBC:** Monitor periodically if used long-term (rare risk of anemia/blood dyscrasias).
## Clinical Pearls
* **GI Side Effects:** Diarrhea is uniquely more common with mefenamic acid than with other NSAIDs. If diarrhea occurs, consider dose reduction or discontinuation.
* **Duration:** Efficacy is most supported for short-term use. Chronic use is generally avoided due to the higher safety profile of other NSAIDs.
* **Administration:** Take with food or milk to minimize gastrointestinal irritation.
* **Cardiovascular Warning:** Like all non-aspirin NSAIDs, it carries a boxed warning for increased risk of serious cardiovascular thrombotic events.
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**Educational Disclaimer:** This information is for educational purposes only and does not replace professional clinical judgment. Always consult the most current product monograph, institutional guidelines, or a reliable drug database (e.g., Lexicomp, Micromedex) before prescribing or administering medication.
